Smoking cessation services are an unmet need among the homeless, who smoke at rates more than 3 times the national estimate; successful interventions in this underserved population have the potential for improving individual and public health. Contingency management (CM) is a behavioral intervention with efficacy in a number of substance use disorder populations, including smokers. However, no known studies have evaluated the effect of CM in homeless smokers. We plan to examine smoking-related outcomes in homeless treatment-seeking smokers (N = 70) randomized to standard care smoking cessation (transdermal nicotine replacement therapy [NRT] + standard counseling + carbon monoxide [CO] monitoring) or standard care plus CM (NRT + standard counseling + CO monitoring + CM) conditions. Standard counseling and CO monitoring will occur for the first 4 weeks, with NRT use continuing through week 8. Participants in both conditions will meet with study staff up to twice daily on weekdays for biochemical verification of smoking status. Participants in the CM condition will have the opportunity to earn prizes for negative breath samples (CO d 4 ppm) up to twice daily on weekdays, with average expected reinforcement of about $408. Participants in the standard care condition will receive $2 gift cards for CO sample submissions up to twice daily on weekdays, noncontingent on smoking status. Follow-up assessments will be scheduled at 5, 9, 12, and 24 weeks post-quit date. We will use urine cotinine samples to verify smoking status at study intake and the 12- and 24-week follow-ups. CO breath samples will be collected at all visits. Primary treatment outcomes will include percent negative samples submitted, longest duration of abstinence achieved during treatment, and point prevalence rates of abstinence. We expect that participants randomized to CM will have better outcomes across these indices compared to those in standard care. Abbreviations: CM = Contingency management CO = Carbon monoxide CPD = Cigarettes per day LDA = Longest duration of continuous verified abstinence NRT = Nicotine replacement therapy PPM = Parts per million SC = Standard care PUBLIC HEALTH RELEVANCE: Smoking rates in the homeless population are more than 3 times the national smoking rate. This project evaluates the addition of contingency management to standard treatment to improve smoking outcomes in homeless smokers. Effective smoking cessation treatment for homeless smokers will benefit both the smokers' health and the public, on whom much of the homeless healthcare burden falls.